Axial piston pump auxiliary cam assembly

ABSTRACT

An auxiliary cam assembly for an axial piston pump includes an auxiliary cam plate and an auxiliary cam retainer. The auxiliary cam plate is configured to be coupled a rotatable shaft. A central shaft opening extends through the auxiliary cam plate. A plurality of piston openings surround the central opening and extend through the auxiliary cam plate. A circumferential cut is formed in and extends around the outer peripheral surface of the auxiliary cam plate. The auxiliary cam retainer has a plurality of ramps formed therein, and each ramp slopes upwardly from a first end to a second end. A plurality of substantially flat pads are disposed between each of the ramps, and each pad extends between the first end of one ramp and the second end of another ramp.

TECHNICAL FIELD

The present invention generally relates to axial piston pumps, and more particularly relates to an auxiliary cam plate and auxiliary cam retainer that are configured to induce lubrication of the auxiliary cam plate-to-auxiliary cam retainer interface.

BACKGROUND

Axial piston pumps are used in myriad systems and environments. An axial piston pump generally includes a housing, a rotor, a port plate, a hanger (or swash plate), and an auxiliary cam assembly. The rotor is rotationally mounted within the housing, and has a number of piston bores formed therein. A piston is movably inserted into each one of the piston bores. The port plate is non-rotationally mounted within the housing adjacent one end of the rotor, and includes a low-pressure side and a high-pressure side. The hanger is also non-rotationally mounted in the housing but may be allowed to pivot about a central axis ninety degrees from the rotor axis. The hanger is disposed at an opposite end of the rotor and at an angle relative to the rotational axis of the rotor. The auxiliary cam assembly is coupled to the angularly disposed hanger and to each of the pistons.

With the above-described configuration, when the rotor is rotated the auxiliary cam assembly successively pulls the pistons from, while the hanger pushes the pistons back into, the piston bores. More specifically, pump is configured so that the pistons are pulled from the piston bores on the low pressure side of the port plate, thereby drawing fluid into the bores, and are pushed into the piston bores on the high pressure side of the port plate, thereby forcing fluid out of the piston bores.

The auxiliary cam assembly includes an auxiliary cam plate and an auxiliary cam retainer. The auxiliary cam plate is mounted on, and rotates with, the shaft, and includes a plurality of piston openings into which an end of each piston is inserted. The ends of each piston are retained via piston shoes that are inserted, one each, into a piston opening. The back flange of each piston shoe reacts its load on the auxiliary cam plate when its associated piston is being pulled from the piston bore. The rotating auxiliary cam plate reacts this load and that of the other pistons onto the auxiliary cam retainer. The auxiliary cam retainer is non-rotationally mounted within the housing or the hanger, and engages the auxiliary cam plate near its periphery.

The interface of the auxiliary cam plate and the auxiliary cam retainer can wear and significantly impact overall pump reliability. Hence, it is desirable to lubricate this interface. The fluid surrounding the interface is at relatively low case pressure. Simply relying on leakage of fluid into the interface is insufficient to provide adequate lubrication at operating conditions. Presently, known means of providing adequate lubrication involve the undesirable use of extensive channeling and/or galleries.

Hence, there is a need for providing a way to adequately lubricate the interface of the auxiliary cam plate and auxiliary cam retainer in an axial piston pump that does not rely on extensive channeling and/or galleries. The present invention addresses at least this need.

BRIEF SUMMARY

In one embodiment, an auxiliary cam assembly for an axial piston pump includes an auxiliary cam plate and an auxiliary cam retainer. The auxiliary cam plate is configured to be coupled to a rotatable shaft and includes a main body having a first side, a second side, and an outer peripheral surface. A central shaft opening extends between the first side and the second side for receiving the rotatable shaft. A plurality of piston openings surround the central opening and extend between the first side and the second side. Each piston opening is for receiving at least a portion of a piston. A circumferential cut is formed in and extends around the outer peripheral surface of the auxiliary cam plate. The auxiliary cam retainer has an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface. At least a portion of the engagement side contacts the auxiliary cam plate first side. A plurality of ramps are formed in the engagement side. Each ramp slopes upwardly from a first end to a second end. A plurality of substantially flat pads are integrally formed on the engagement side and are disposed between each of the ramps. Each substantially flat pad extends between the first end of one ramp and the second end of another ramp.

In another embodiment, an axial piston pump includes a pump housing, a rotor, a plurality of pistons, a hanger, an auxiliary cam plate, and an auxiliary cam retainer. The rotor is rotationally mounted within the pump housing, and includes a shaft and a plurality of axial piston bores. The rotor is configured, upon receipt of an input torque on the shaft, to rotate about a rotational axis. Each piston is movably disposed within, and extends from, one of the plurality of axial piston bores. The hanger is non-rotationally mounted within the pump housing and has a opening through which the shaft extends. The hanger is disposed at an angle relative to the rotational axis. The auxiliary cam plate is disposed adjacent the hanger, and is coupled to the shaft and configured to rotate therewith. The auxiliary cam plate includes a main body having a first side, a second side, and an outer peripheral surface. A central opening extends between the first side and the second side, and the shaft extends through the central opening. A plurality of piston openings surround the central opening and extend between the first side and the second side. Each piston extends at least partially into one of the piston openings. A circumferential cut is formed in and extends around the outer peripheral surface of the auxiliary cam plate. The auxiliary cam retainer is coupled to the hanger and has an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface. At least a portion of the engagement side contacts the auxiliary cam plate first side. A plurality of ramps are formed in the engagement side, and each ramp slopes upwardly from a first end to a second end. A plurality of substantially flat pads are integrally formed on the engagement side and are disposed between each of the ramps. Each substantially flat pad extends between the first end of one ramp and the second end of another ramp.

Furthermore, other desirable features and characteristics of the axial piston pump and auxiliary cam assembly will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 depicts a cross section view of an embodiment of an axial piston pump that may include the present invention;

FIG. 2 depicts a cross section view of an embodiment of a hanger and auxiliary cam assembly that may be used in the axial piston pump of FIG. 1;

FIG. 3 depicts a perspective plan view of an embodiment of an auxiliary cam assembly;

FIG. 4 depicts a perspective plan view of an embodiment of the auxiliary cam plate depicted in FIG. 3;

FIGS. 5A and 5B depict close-up cross section views of a portion of the auxiliary cam plate depicted in FIG. 4, illustrating different configurations of a groove that may be formed therein;

FIGS. 6 and 7 depict end and cross section views, respectively, of an embodiment of the auxiliary cam retainer depicted in FIG. 3; and

FIG. 8 depicts a simplified cross section view of a portion of a portion of the auxiliary cam retainer depicted in FIGS. 6 and 7.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.

Referring first to FIG. 1, a cross section view of an embodiment of an axial piston display pump 100 is depicted, and includes a pump housing 102, a rotor 104, a port plate 106, a plurality of pistons 108 (only one visible), and a hanger assembly 110. The pump housing 102 may be variously configured and implemented. In the depicted embodiment, however, the pump housing 102 includes a lower housing section 101 and an upper housing section 103 that are coupled together to form the pump housing 102.

The rotor 104 is rotationally mounted within the pump housing 102 via a rotor bearing 112, and includes a shaft 114 and a plurality of axial piston bores 116. It will be appreciated that the shaft 114 may be formed integrally with the rotor 104, or formed separate from the rotor 104 and subsequently coupled thereto. In either case, it is seen that the shaft 114 is also preferably rotationally supported in the pump housing 102 via a thrust bearing 118. The shaft 114 is adapted to receive an input torque from a suitable torque source, such as a motor or engine. The rotor 104 is configured, upon receipt of the input torque on the shaft 114, to rotate about a rotational axis 122.

The axial piston bores 116 each include a fluid port 124 through which fluid ingresses and egresses during operation of the pump 100. The fluid that ingresses and egresses the fluid ports 124 does so via the port plate 106, which includes a fluid inlet port 126 and a fluid outlet port 128. The fluid inlet port 126 and fluid outlet port 128 are in fluid communication with a fluid inlet passage 132 and a fluid outlet passage 134, respectively, formed in the lower section 101 of the pump housing 102.

The pistons 108 are each movably disposed in, and extend partially from, one of the axial piston bores 116. Each piston 108 includes a first end 136, a second end 138, and an internal fluid passage 142 that extends between the first and second ends 136, 138. The internal fluid passage 142, as will be described further below, allows a portion of the fluid that is drawn into and discharged from the axial piston bores 116 to flow out the piston second end 138 and act as a lubricant.

The second end 138 of each piston 108 is coupled to the hanger assembly 110, which has an opening 144 through which the shaft 114 extends. As FIG. 1 also clearly depicts, the hanger assembly 110 is disposed at an angle relative to the rotational axis 122 of the rotor 104. A particular preferred embodiment of the hanger assembly 110 is shown more clearly in FIG. 2, and with reference thereto, will now be described in more detail.

The hanger assembly 110 includes a hanger 202 and an auxiliary cam assembly 204. The hanger 202 is non-rotationally mounted within the pump housing 102. As is generally known, the angle at which the hanger 202 (and concomitantly the auxiliary cam assembly 204) is disposed, determines the overall stroke of the pistons 108 and thus the flow rate of the pump 100. In the embodiment depicted in FIG. 1, the hanger angle, and thus the flow rate, may be varied via a control piston 146 (see FIG. 1). Whether or not the hanger 202 is adjustable, it includes a recess 206 in which at least a portion of the auxiliary cam assembly 204 is disposed.

The auxiliary cam assembly 204, at least in the depicted embodiment, includes a cam plate 208, an auxiliary cam plate 212, and an auxiliary cam retainer 214. The cam plate 208 is fixedly coupled within the recess 206, and provides a surface 216 that piston shoes 218 movably engage. The piston shoes 218 (for clarity, only one depicted in FIG. 2) are each mounted on the second end 138 of one of the pistons 108. As FIG. 2 also depicts, each piston shoe 218 includes a fluid flow port 222 and a back flange 224. As was noted above, during pump operation a portion of the fluid that is drawn into and discharged from the axial piston bores 116 flows out the second end 138 of each piston 108. This fluid in turn flows through the fluid flow ports 222 in each piston shoe 218, and lubricates the interface of the piston shoe 218 and the cam plate 208.

The auxiliary cam plate 212 is mounted on, and rotates with, the shaft 114. More specifically, and as shown more clearly in FIGS. 3 and 4, the auxiliary cam plate 212 includes a main body 302 having a first side 402 (see FIG. 4), a second side 304, and an outer peripheral surface 306. A central opening 308 is formed in the main body 302 and extends between the first side 402 and the second side 304. The shaft 114 (not shown in FIGS. 2-4) extends through the central opening 308. A plurality of piston openings 312 are also formed in the main body 302 and extend between the first side 402 and the second side 304. The plurality of piston openings 312 surround the central opening 308, and each has a portion of one of the pistons 108 disposed therein. More specifically, and with reference once again to FIG. 2, the second end 138 of each piston 108 partially extends into one of the piston openings 312, and is retained therein via one of the piston shoes 218. The back flange 224 of each piston shoe 218 is disposed between the cam plate 208 and the second side 304 of the auxiliary cam plate 212. The auxiliary cam plate 212, and thus each piston shoe 218, is retained within the hanger recess 206 via the auxiliary cam retainer 214. Although the depicted auxiliary cam plate 212 includes seven piston openings 312, it will be appreciated that the auxiliary cam plate 212 may include more or less than this number.

The auxiliary cam retainer 214 is coupled to the hanger 202 and thus, like the hanger 202, is non-rotationally mounted within the pump housing 102. With reference to FIGS. 6 and 7, it may be seen that the auxiliary cam retainer 214 has an engagement side 602, a non-engagement side 702, an inner peripheral surface 604, and an outer peripheral surface 606. Preferably, the auxiliary cam retainer 214 is coupled to the hanger 202 via suitable fastening hardware, such as the bolts 314 depicted in FIG. 3. To facilitate this, the depicted auxiliary cam retainer 214 the outer peripheral surface 606 defines a plurality of radially extending flanges 608, each having a fastener opening 612 formed therein. The inner peripheral surface 604 has a diameter that is slightly less than the outer diameter of the auxiliary cam plate 212. Thus, as shown most clearly in FIG. 2, at least a portion of the engagement side 602 contacts the auxiliary cam plate first side 402 near its outer peripheral surface 306.

During operation of the pump 100, as each piston 108 is being pulled from its associated piston bore 116, the load on each associated piston shoe 218 is reacted onto the rotating auxiliary cam plate 212. This load, and that of the other pistons 108, is in turn reacted onto the auxiliary cam retainer engagement side 602. As will now be described in more detail, the auxiliary cam plate 212 and auxiliary cam retainer 214 are configured such that the fluid within the pump housing 102, which is at a relatively low pressure, lubricates the interface of the auxiliary cam plate 212 and auxiliary cam retainer 214.

The auxiliary cam retainer 214, and more specifically the engagement side 602 of the auxiliary cam retainer 214, has a plurality of ramps 614 formed therein, and a plurality of substantially flat pads 616 integrally formed thereon. As shown more clearly in FIG. 8, each ramp 614 slopes upwardly from a first end 802 to a second end 804, and each pad 616 extends between the first end 802 of one ramp 614 and the second end 804 of a successive ramp 614. The first end 802 of each ramp 614 is offset from its second end 804 by a predetermined depth (d). Although this predetermined depth may vary, in the depicted embodiment the depth is preferably in the range of 0.0005 to 0.0015 inches, and is most preferably 0.001 inches. These parameters are based on jet fuel as the working fluid and can be expected to change for other liquids.

The ramps 614 are also preferably formed to slope upwardly from the first end 802 to the second end 804 at a predetermined, fixed angle (θ). This predetermined, fixed angle may vary, but is preferably in the range of 8 to 20 arc minutes, with 7-10 arc minutes being more preferred, and 10 arc minutes being most preferred. It is further noted that the ramps 614 preferably slope upwardly in the direction of rotation of the auxiliary cam plate 212. Thus, as FIG. 8 depicts, the auxiliary cam plate 212 will preferably rotate in the direction of arrow 806.

Returning once again to FIG. 6, it is noted that the ramps 614 and pads 616 may be formed on the entire auxiliary cam retainer engagement side 602, or on only a portion thereof. In the depicted embodiment, the ramps 614 and pads 616 are formed on the entire auxiliary cam retainer engagement side 602. In other embodiments, however, these features may be formed only in the region centered about piston top dead center, and at +/−45 to 90 degrees, with +/−60 degrees being preferred. It is additionally noted that the ramps 614 may be evenly or unevenly distributed around the engagement side 602 of the auxiliary cam retainer 214, and that the length of each ramp 614, between its first end 802 and its second end 804, may be equal or unequal.

It is on the top of each of the substantially flat pad 616 where the resulting hydrodynamic fluid film supports the load of the rotating auxiliary cam plate 212 during operation. Each pad 616 is preferably formed with an equal, predetermined circumferential width (Wc) (see FIG. 8). Although the circumferential width may vary, it is preferably in the range of 1 to 6 degrees, with 4 degrees being most preferred.

The above-described ramps 614 and pads 616 that are formed in the auxiliary cam retainer 214 facilitate fluid induction and the formation of a hydrodynamic layer between the auxiliary cam plate 212 and auxiliary cam retainer 214. However, the auxiliary cam plate 212 and auxiliary cam retainer 214 are asymmetrically loaded during pump operation. As a result, the fluid that could form the hydrodynamic fluid film is bled off, thereby eliminating the effectiveness of the ramps 614 and pads 616. To alleviate this effect, the compliance of auxiliary cam plate 212 is controlled.

More specifically, and with reference to FIGS. 4, 5A, and 5B, the compliance of the auxiliary cam plate 212 is controlled via a circumferential cut 404 that extends around the outer peripheral surface 306 of the auxiliary cam plate 212. The circumferential cut 404 may be variously configured to control the compliance of the auxiliary cam plate 212. For example, the circumferential cut 404 may be configured as a groove, such as the one depicted in FIG. 5A, or it may be configured as an undercut, such as the one depicted in FIG. 5B. When configured as a groove, the circumferential cut 404 is preferably disposed midway between the first side 402 and the second side 304 of the auxiliary cam plate 212, and has a predetermined depth (D). When configured as an undercut, the circumferential cut 404 also has a predetermined depth (D), and is disposed such that the larger diameter portion engages the auxiliary cam retainer 214.

No matter the specific configuration of the circumferential cut 404, it is noted that the predetermined depth (D) may vary, and is selected to provide the desired compliance. It is additionally selected so that the circumferential cut 404 does not penetrate into the piston openings 312, and at least overhangs the inner peripheral surface 604 of the auxiliary cam retainer 214. Though not depicted, in some embodiments, circumferential cut 404 may be scalloped between piston openings 312 to enhance compliance control. It will nonetheless be appreciated that the specific configuration and dimensions of the circumferential cut 404 may be determined on a case-by-case basis to achieve the desired compliance, and thereby assure that the auxiliary cam plate 212 and auxiliary cam retainer 214 are maintained sufficiently parallel to allow the pads 616 to create a load carrying hydrodynamic fluid film.

The auxiliary cam plate 212 and auxiliary cam retainer 214 described herein together provide a means to adequately lubricate the interface of these components that does not rely on extensive channeling and/or galleries. The specific configuration and dimensions of these components may be varied to attain the desired lubricity using lubricating fluids of varying viscosity.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. An auxiliary cam assembly for an axial piston pump, comprising: an auxiliary cam plate configured to be coupled a rotatable shaft and including a main body having a first side, a second side, and an outer peripheral surface; a central shaft opening extending between the first side and the second side for receiving the rotatable shaft; a plurality of piston openings surrounding the central opening and extending between the first side and the second side, each piston opening for receiving at least a portion of a piston; a circumferential cut extending around the outer peripheral surface of the auxiliary cam plate; an auxiliary cam retainer having an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface, at least a portion of the engagement side contacting the auxiliary cam plate first side; a plurality of ramps formed in the engagement side, each ramp sloping upwardly from a first end to a second end; and a plurality of substantially flat pads integrally formed on the engagement side and disposed between each of the ramps, each substantially flat pad extending between the first end of one ramp and the second end of another ramp.
 2. The assembly of claim 1, wherein: the auxiliary cam plate and the auxiliary cam retainer each exhibit a compliance under load; and the compliance of the auxiliary cam plate is substantially matched to that of the auxiliary cam retainer via the circumferential cut.
 3. The assembly of claim 1, wherein: the circumferential cut is configured as a circumferential groove; and the circumferential groove is disposed midway between the first side and the second side of the auxiliary cam plate.
 4. The assembly of claim 1, wherein the circumferential cut is configured as an undercut.
 5. The assembly of claim 1, wherein the circumferential cut has a predetermined depth.
 6. The assembly of claim 1, wherein the ramps and pads are evenly distributed around the engagement side of the auxiliary cam retainer.
 7. The assembly of claim 1, wherein the ramps and pads are unevenly distributed around the engagement side of the auxiliary cam retainer.
 8. The assembly of claim 1, wherein: each ramp has a length between its first end and its second end; and the length of each ramp is equal.
 9. The assembly of claim 1, wherein: each ramp has a length between its first end and its second end; and the length of each ramp is not equal.
 10. The assembly of claim 1, wherein each ramp slopes upwardly from its first end to its second end at a predetermined, fixed angle.
 11. The assembly of claim 10, wherein the predetermined, fixed angle is between 8 and 20 arc minutes.
 12. The assembly of claim 1, wherein the first end of each ramp is offset its second end by a predetermined depth.
 13. The assembly of claim 12, wherein the predetermined depth is between 0.0005 inches and 0.0015 inches.
 14. The assembly of claim 1, wherein each pad has a predetermined circumferential width.
 15. The assembly of claim 14, wherein the predetermined circumferential width is between 1 and 6 degrees.
 16. An axial piston pump, comprising: a pump housing; a rotor rotationally mounted within the pump housing, the rotor including a shaft and a plurality of axial piston bores, the rotor configured, upon receipt of an input torque on the shaft, to rotate about a rotational axis; a plurality of pistons, each piston movably disposed within, and extending from, one of the plurality of axial piston bores; a hanger non-rotationally mounted within the pump housing and having a opening through which the shaft extends, the hanger disposed at an angle relative to the rotational axis; an auxiliary cam plate disposed adjacent the hanger, the auxiliary cam plate coupled to the shaft and configured to rotate therewith, the auxiliary cam plate including a main body having a first side, a second side, and an outer peripheral surface, a central opening extending between the first side and the second side, the shaft extending through the central opening; a plurality of piston openings surrounding the central opening and extending between the first side and the second side, each piston extending at least partially into one of the piston openings; a circumferential cut formed in and extending around the outer peripheral surface of the auxiliary cam plate; and an auxiliary cam retainer coupled to the hanger and having an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface, at least a portion of the engagement side contacting the auxiliary cam plate first side, a plurality of ramps formed in the engagement side, each ramp sloping upwardly from a first end to a second end; and a plurality of substantially flat pads integrally formed on the engagement side and disposed between each of the ramps, each substantially flat pad extending between the first end of one ramp and the second end of another ramp.
 17. The pump of claim 16, wherein: the auxiliary cam plate and the auxiliary cam retainer each exhibit a compliance under load; and the compliance of the auxiliary cam plate is substantially matched to that of the auxiliary cam retainer via the circumferential cut.
 18. The pump of claim 16, wherein: each ramp slopes upwardly from its first end to its second end at a predetermined, fixed angle; and the first end of each ramp is offset its second end by a predetermined depth.
 19. The pump of claim 16, wherein each pad has a predetermined circumferential width.
 20. The pump of claim 16, wherein: the rotor is configured to rotate about the rotational axis in a first direction; and each ramp slopes upwardly in the first direction. 